It’s really not a good time to be a bluefin tuna. Highly prized and globally overfished, the fish now has a new nemesis: nuclear radiation. Samples of bluefin tuna caught just outside of San Diego, California, have been found to contain radioactivity that can definitely be traced to Japan’s Fukushima nuclear reactors.

As Bloomberg reports, 15 Pacific bluefin caught in California waters last August had levels of radioactive cesium 10 times higher than in fish caught in previous years. That gives researchers “unequivocal evidence” that the radiation came from Fukushima, according to a study published yesterday in the Proceedings of the National Academy of Sciences.

If you’ve been eating sushi, don’t panic. The levels aren’t considered a danger to humans, the scientists say, and will likely decrease with time as the radiation is diluted by the ocean.

About 3,500 terabecquerels of cesium 134 and 3,600 terabecquerels of cesium 137 may have leaked into the ocean after the meltdown of three reactors at the Fukushima Dai-Ichi nuclear plant following the earthquake and subsequent tsunami last March, operator Tokyo Electric Power Co. (9501) said in a statement last week.

The National Academy of Sciences study compared bluefin with fish caught before the disaster, which showed no trace of cesium 134 and only background levels of cesium 137 from nuclear weapons testing, reports Bloomberg.

It’s another disastrous development for the bluefin tuna, which has seen its numbers decline dramatically as global sushi consumption has risen. Demand for the fish is at an all-time high: Earlier this year, a 593-pound whopper brought in a staggering bid of nearly $740,000 from Tokyo-based Kiyomura Company.

Because tuna is a predator fish, its levels of radiation depend largely on the amount of radiation in the smaller fish it preys on.

“However, certain small fish around Japan showed very high levels after the accident,” Daniel Madigan, the study’s co-author and researcher at Hopkins Marine Station at Stanford, told Bloomberg. “If certain larger predators happen to feed on these prey, higher levels than we observed may be possible.”

Are you worried about radiation levels in fish? Let us know in comments.

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